Heat sealed package

ABSTRACT

The invention relates to a package for a sterilised disposable article, the package having opposing base materials bonded together along marginal portions by a heat sealed adhesive and peelable apart to open the package. One of the base materials is paper which has been neutrally sized to prevent absorption of the adhesive. The outer surface of the paper is preferably machine glazed for porosity and pore size control. The adhesive may be applied all over the unglazed surface of the paper but in a discontinuous form to permit passage of a sterilising gas into the sealed package.

United States Patent [1 1 Jones [451 Sept. 2, 1975 1 HEAT SEALED PACKAGE[75] Inventor: Christopher Ian Jones, Keynsham,

near Bristol, England 22 Filed: Apr. 27, 1973 21 App]. NO.Z 355,092

[56] References Cited UNITED STATES PATENTS 3,217,871 11/1965 Lee260/632 3,485,638 12/1969 Benson 117/154 3,578,239 5/1971 Periman 229/48T 3,595,465 7/1971 Vaillancoutt 206/363 3,685,720 8/1972 Brady 206/4383,779,791 12/1973 Ploetz 117/154 FOREIGN PATENTS OR APPLICATIONS 802.35610/1958 United Kingdom 802,357 10/1958 United Kingdom PrimaryExuminer-William R. Trenor Attorney, Agent, or FirmLarson, Taylor andHinds 5 7 ABSTRACT The invention relates to a package for a steriliseddisposable article, the package having opposing base materials bondedtogether along marginal portions by a heat sealed adhesive and peelableapart to open the package. One of the base materials is paper which hasbeen neutrally sized to prevent absorption of the adhesive. The outersurface of the paper is preferably ma chine glazed for porosity and poresize control. The adhesive may be applied all over the unglazed surfaceof the paper but in a discontinuous form to permit passage of asterilising gas into the sealed package.

6 Claims, No Drawings HEAT SEALED PACKAGE This invention relates to aheat sealed package having opposing base materials which are heat sealedtogether along marginal portions but can be peeled apart to open thepackage. at least one of the base materials being paper. The inventionalso relates to a paper base material.

The invention is particularly but not exclusively applicable to heatsealed packages containing disposable surgical instruments, syringes orother articles used in surgery or medicine. Such packages are requiredto meet a number of conditions, eg they must allow their contents to besterilised after heat sealing, they must retain their contents in asterilised condition until opened, and they must be openable in such amanner as to permit their contents to be removed without contamination.The last condition may be met by providing a peelable heat seal whichpermits a smooth and clean peeling apart of the opposing base materialsof the package. The present invention provides a package which satisfiesthe above conditions.

In this specification the term neutrally sized is used to means sizedunder neutral conditions with a pH value in the range 7.2 to 8.3inclusive and using an alkyl ketene dimer as the sizing agent.

According to one aspect of the invention there is provided a packagecomprising opposing base materials bonded together along marginalportions by means of a heat sealed adhesive and peelable apart to openthe package. wherein one of the base materials is neutrally sized paper,

According to another aspect of the invention, in a preferred embodimenta base material for the package is paper which has been neutrally sized,machine glazed on one surface, and has all over its unglazed surface aheat sealable adhesive applied in a discontinuous form.

Machine glazed paper is paper which has one surface made smooth, forexample by drying the paper on a heated polished metal cylinder formingpart of a papermaking machine. The other or unglazed surface of thepaper remains relatively rough.

Machine glazed paper has good strength characteristics and can be madeto a specified porosity and maximum pore size. Where a package is to besterilised internally by means of ethylene oxide or a mixture ofethylene oxide and inert gas, the paper base material preferably has aBendtsen porosity between the limits of 601 20 cc/min. To minimise therisk of bacteria entry into the sealed package, the paper should have abasic weight not less than 50g/m2, and preferably not less than 55g/m2,whilst the maximum pore size should be not greater than mym. Maximumpore size may be measured by the method described in Interpretation ofPaper Properties in Terms of Structure by Dr. H. Corte and Dr. 0. J.Kallmes, in the Transactions of the Oxford Symposium 1961, The Formationand Structure of Paper", published by the Technical Section of theBritish Paper & Board Makers Association (Incorporated), London, E.C.4.

For a gas-sterilised package it is not necessary for the other basematerial to be porous. This other base material may be either a film ofa thermoplastics material, or a laminate comprising two or more layersof similar or dissimilar plastics materials, or a plastics coating upona porous substrate such as for example a polyethylene coated paper,whether made by laminating polyethylene film to paper or by anextrustion coating process. For gas sterilisation purposes it isnecessary to have the coating on the porous base material either in adiscontinuous form or of such a gas permeability that the requiredBendsten porosity is achieved.

Alternatively. the other base material may be porous, in which case itmay be a paper with a smooth finish on one surface. Such a finish may beproduced by machine glazing, by supercalendering, or by glassinecalendering. This porous material should have a porosity and maximumpore size which are not greater that those of the neutrally sized paperforming the opposite base material in the gas-sterilisable package.

As a further alternative in a gas-sterilisable package, the porous basematerial may be a non-woven fabric or paperlike material but with thesame relative limitations on porosity and maximum pore size as justquoted.

NEUTRAL SIZING AGENTS These agents are alkyl ketene dimers. An exampleof such an agent is AQUAPEL ketene dimer which is marketed by theHercules Powder Co. Ltd., of London. England.

ADHESIVES These may be beat seal compositions such as solventbasedthermoplastic coating compositions based on ethylene/vinyl acetatecopolymers. Alternatively, the adhesives may be water-based dispersionsof ethylene/- vinyl acetate intcrpolymers and may contain wax or othermodifiers, or the adhesive may be a hot-melt adhesive which may containpolyisobutylene and paraffin wax. The weight of adhesive coating isbetween 1 and 20 gms per square metre and preferably is between 2 and 10gms per square metre in the coated area, depending on the second basematerial.

EXAMPLE 1 Bleached kraft paper forming a first base material wasneutrally sized and then machine glazed on one surface. The Bendtdenporosity was between the limits of 60-120 cc/min and the maximum poresize was not greater that 10 mym. The paper was coated all over itsunglazed surface with a heat sealable lacquer adhesive, sold under thetrade name ADCOTE by Morton- Williams Limited, of Hounslow, Middlesex,England which is a solvent-based thermoplastic material. The adhesivewas applied in a grid form by means of a gravure cylinder and thendried. The advantage of coating the paper all over its unglazed surfacein a discontinuous form is that the paper may be used for packages ofdifferent sizes or sealing areas.

With the paper held horizontal, coated side upwards, an article to bepackaged was placed on the paper and then a second base material, in theform of a nonporous laminate. of 12.5 mym polyester film/38 mympolyethylene film, was placed over the article with its polyethylenefilm facing downwards and heat sealed along its marginal portions in aSentinel heat sealer to the opposing paper base material to form asealed pouch-type packaging containing the article. The interior of thesealed package was gas sterilised, using ethylene oxide or a knowngaseous mixture of ethylene oxide and inert gas.

The neutral sizing agent prevented absorption of the adhesive by thepaper base material both during application and subsequent'heat sealing.However the relative roughness of the unglazed surface of the paperassisted the bonding of the adhesive to the paper and in the sealedpackage the bond strength of the heat seal was found to be commerciallyacceptable. The discontinuous form of the applied adhesive made itpossible to penetrate the whole area of the package with the sterilisinggas. The package was then peeled open in a smooth manner and with aclean peel. i.e.' without visible transfer of fibre from the rough papersurface to the polyethylene film, thereby minimising possiblecontamination of the sterilised article in the package.

The external glazed surface of the package was suitable for good qualityprinting.

EXAMPLE II EXAMPLE II] A package was made as described in Example Iexcept that the non-porous laminate was replaced by a bleached kraftpaper having the same characteristics and treatment as described in thefirst paragraph of Example but without the adhesive, the first paperbase material being heat sealed to the unglazed surface of the secondpaper base material.

EXAMPLE IV A package was made as described in Example Ill except thatthe heat sealable lacquer adhesive was coated on to the machine glazedsurface of the first paper base material.

EXAMPLE V Packages were made as described in Example I, Example lll andExample lV respectively, except that the adhesive used was a water-basedethylene vinyl acetate/wax dispersion thermoplastic coating sold underthe trade name ELVAX-D by the Du Pont Company of London, England.

EXAMPLE Vl Packages were made as described in Example I and Example lllrespectively, except that the heat sealable lacquer adhesive applied tothe first base material was a hot melt adhesive sold under the tradename LUNA- MELT PS by Industrial Waxes Limited of London, England.

EXAMPLE v11 A package was made as described in Example 1 except that gassterilisation was replaced by Gamma irradiation at 5 megarads.

ln Examples Ill-VII the bond strength of the heat seal was commerciallyacceptable. Furthermore, when the opposing base materials were peeledapart they separated in a smooth manner and with a clean peel.

' The invention is not limited to pouch-type packages.

For example the neutrally sized paper base material may be peelably heatsealed to an open top rigid container so as to close it, the containerbody being of thermo-formed untreated unplasticized polyvinyl chloride,or cellulose acetate, or a laminate of polyethylene and untreatedunplasticized polyvinyl chloride or cellulose acetate.

' Instead of applying the adhesive all over one surface of the firstbase material, it may be applied to the sealing areas only, in whichcase it need not be applied in discontinuous form.

I claim:

1. A package comprising opposing base materials bonded together atmarginal portions by means of a heat sealed adhesive which allows thebase materials to be peeled apart cleanly to open the package, one ofthe base materials comprising paper which has been sized under neutralconditions with a pH value in the ranges 7.2 to 8.3 inclusive using analkyl ketene dimer, and which has a machine glazed surface.

2. a package according to claim 1, wherein the machine glazed surface ofthe paper base material is an outer surface of the package.

3. A package according to claim 1, wherein the adhesive was applied tothe unglazed surface of the neutrally sized paper in a discontinuousform to allow a sterilising gas to pass through it.

4. A package according to claim 3, wherein the adhesive was applied ingrid form or dotted form.

5. A package according to claim 1, wherein the neutrally sized paper,excluding the sizing, has a weight not less than S5g/m a maximum poresize not greater than 10 mym, and a Bendtsen porosity of -120 cc/min.

6. A base material for a package as claimed in claim 3, wherein the basematerial is a neutrally sized paper which has been sized under neutralconditions with a pH value in the range 7.2 to 8.3 inclusive using analkyl ketene dimer, which has been machine glazed on one surface, andwhich has, on its unglazed surface, a heat sealable adhesive applied ina discontinuous form.

1. A PACKAGE COMPRISING OPPOSING BASE MATERIALS BONDED TOGETHER ATMARGINAL PORTIONS BY MEANS OF A HEAT SEALED ADHESICE WHICH ALLOWS THEBASE MATERIAL TO BE PEELED APART CLEANLY TO OPEN THE PACKAGE, ONE OF THEBASE MATERIALS COMPRISING PAPER WHICH HAS BEEN SIZED UNDER NEUTRALCONDITIONS WITH A PH VALUE IN THE RANGES 7.2 TO 8.3 INCLUSIVVE USING ANALKYL KETENE DIMER, AND WHICH HAS A MACHINE GLAZED SURFACE.
 2. a packageaccording to claim 1, wherein the machine glazed surface of the paperbase material is an outer surface of the package.
 3. A package accordingto claim 1, wherein the adhesive was applied to the unglazed surface ofthe neutrally sized paper in a discontinuous form to allow a sterilisinggas to pass through it.
 4. A package according to claim 3, wherein theadhesive was applied in grid form or dotted form.
 5. A package accordingto claim 1, wherein the neutrally sized paper, excluding the sizing, hasa weight not less than 55g/m2, a maximum pore size not greater than 10mym, and a Bendtsen porosity of 60-120 cc/min.
 6. A base material for apackage as claimed in claim 3, wherein the base material is a neutrallysized paper which has been sized under neutral conditions with a pHvalue in the range 7.2 to 8.3 inclusive using an alkyl ketene dimer,which has been machine glazed on one surface, and which has, on itsunglazed surface, a heat sealable adhesive applied in a discontinuousform.